Choosing the most suitable design of magnetic
separator is governed by four objectives
aggregate and quarrying applications, as
they can be xed on to a track-mounted
mobile crusher for the removal of rebar
from crushed concrete. For recycling
applications, the Eriez Eddy Current
Separator can be used to remove nonferrous
contaminants from a range of
materials; for example, its RevX-E ST22-
80 for removal of aluminum and copper
from glass, plastic, wood and bottom-ash
products.
Other products include the HI1000-
65 magnetic lter, which is used for the
puri cation of non-metallic minerals,
such as silica sands and quartz sands, as
well as the RE (rare earth) roll separator,
model RE300-60-3V, most used in the
ceramics and minerals industry as a
puri cation process for feldspar.
HOW TO SPECIFY
According to Bunting, choosing the most
suitable design of magnetic separator
is governed by four objectives. The rst
is the separation objective: to remove
or recover. The second step concerns
the type of ferrous metal, including its
size and shape. The third step considers
the process involved, for example, liquid
or solid state, conveyor or pipelines.
The fourth step covers the installation
process, including available space, as
well as installation and maintenance
requirements.
“These criteria will provide the data
to select a suitable magnetic separator
based upon magnetic strength at
the point of separation,” the Bunting
spokesperson explains. “For example,
for an overband magnet suspended
above a conveyor, the point of separation
is in the conveyed material which will
be at least 250-300mm away from the
face of the magnet where there is the
highest magnetic intensity. Therefore,
a very deep magnetic eld is required.
However, for a simple tube magnet inside
a magnetic liquid lter, the aim is to pass
the liquid and the iron contamination
over or at least very close to the surface
FIXED & BULK MATERIALS HANDLING – MAGNETIC SEPARATORS
of the magnet, where it is attracted and
held. Therefore, this has a very strong
but shallow magnetic eld.”
As for servicing, testing and
maintenance, both Bunting and Eriez
agree that this varies by separator type.
Eriez, for example, manufactures new
rotors, and services and repairs older
rotors for its eddy current separators. It
also o ers aftersales services, such as
calibration and certi cation, as well as
maintenance contracts. “Maintenance
requirements depend on how arduous
the application is,” explains the Eriez
spokesperson. “Typically, any wear items,
particularly in demanding recycling
applications, like belts, rotors, bearings
and drives, will require continuous
monitoring. Eriez recommends that
customers hold these items as strategic
spares on site, should any parts need
urgently replacing.” (Eriez-Europe does
the same).
Meanwhile, Bunting often refurbishes
A permanent overband
magnet mounted on a mobile crusher
old larger magnetic separators
(especially electromagnets) and has
a travelling service team to support
customers at site. “For eddy current
separators, we o er a health check,”
the spokesperson adds, which sees
adjustments and repairs made to keep
equipment running smoothly. This
inspection process often takes place
during the annual plant maintenance
shutdown, or when the plant is
non-operational (www.is.gd/xakilu).
Meanwhile, permanent magnetic
separators, such as the ones used in the
food industry, need checking every 12
months (see box).
Autumn 2020 www.operationsengineer.org.uk 63
Images: Paul Fears Photography
Case study: carrying out a separator audit Bunting engineers conducted a magnetic separator audit at the Jordans Dorset Ryvita
plant in Poole, Dorset, in June, over a three days. The company had not experienced any
problems due to metal contamination, but requested the audit as part of their continued
improvement plan. The rst day was spent assessing the location and recording the
customer identity numbers of all the magnetic separators; 52 were identi ed.
The physical checks of the magnetic separators were conducted on day two and
three, on the weekend to minimise any production downtime. Each separator was
removed from its location and visually inspected. This includes checking welds, and
assessing any wear and damage to the surface.
Stage two involved testing the strength of the separator by placing a magnetic ball
or plate into the magnetic eld and then measuring the force (in kgs) needed to remove
that object from the surface. The test is repeated three times and an average reading
taken. Similar techniques are used to test other designs of magnetic separators such
as plate magnets. Reading the magnetic ux density, measured in Gauss, was avoided
because of the di culty of the measurement.
Results, and recommendations, were presented in a detailed report. “Having an
external review of the magnetic separators really helps the client,” contends Adrian
Coleman, Bunting’s general manager at the Redditch plant. “We conducted the audit
without any assumptions and this freedom enabled us to highlight the areas where
protection was good and also focus attention where they could be improvements.”
Following the audit, the engineering team at Jordans Dorset Ryvita have made several
changes to improve metal removal during production.
/xakilu)
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